1. Field of the Invention
The present invention relates to a method of continuously taking out a twist-free fiber bundle from a cylindrically wound fiber bundle (hereinafter referred to as a fiber bundle package, or more simply, a package) and to a method of manufacturing a resin structure reinforced with long fibers using the thus obtained fiber bundle. More particularly, the invention relates to a method of manufacturing a resin structure reinforced with long fibers in which twisting of a fiber bundle is effectively eliminated, the twisting occurring when the bundle is taken up from the inner side of a plurality of fiber bundle packages each having a hollow cylindrical shape, and the resulting twist-free fiber bundle is impregnated with a resin, thereby eliminating frequent interruption of the manufacture for supplying a starting fiber bundle, achieving a uniform impregnation of the resin into the fiber bundle, and facilitating the manufacture of a resin structure reinforced with long fibers with high strength and consistent properties.
2. Description of the Related Art
Elongated resin structures reinforced with fibers in which thermoplastic resins are reinforced with continuous fibers have mechanical properties much superior to those of structures reinforced with short fibers, and are beneficial because they can be cut and formed into pellets or similar materials. Due to these advantageous features, they have recently become of particular interest. Elongated thermoplastic resin structures reinforced with fibers are generally manufactured by the so-called pultrusion method by impregnating a thermoplastic resin into a continuous fiber bundle for reinforcement while the bundle is passed through a cross-head extrusion die, after which the resin-impregnated fiber bundle is drawn out through the die (U.S. Pat. No. 3,993,726), or by drawing a continuous fiber bundle for reinforcement through a thermoplastic resin melt to wet the bundle and pulling out the wet bundle through a die (Japanese Patent Application Laid-open (kokai) No. 57-181,852). After undergoing the pultrusion method, the structures are cut to a desired size.
Other types of reinforced structures are obtained by reinforcing thermosetting resins with continuous fibers by various methods. For example, in the so-called filament winding method; fibers such as glass roving are coated with a resin before the resin has set and wound around a rotating frame while applying tension,.and then the resin is allowed to set. In the preforming method, a semi-set prepreg is formed. In the pultrusion method, profile extrusion is first performed, after which the extruded product is completely set.
In the manufacture of these resin structures reinforced with long fibers, regardless of whether a thermoplastic resin or a thermosetting resin is used, it is required that a matrix resin be sufficiently impregnated into continuous fiber bundles, and it is important that a matrix resin be uniformly impregnated into the fiber bundles in order to obtain good mechanical properties of the resulting resin structures as well as a good appearance of the final product. To this end, it is a general practice that a fiber bundle which has been bound is loosened while passing through tension bars or rolls under tension, and the loosened fiber bundle is impregnated with a molten or liquid-state resin. In this process, twisting in the fiber bundle causes insufficient loosening of the fiber bundle, which results in uneven impregnation of a resin melt. Moreover, twisting causes easy breakage of fibers of a fiber bundle in a fiber-loosening step, etc. Therefore, twisting must be avoided.
In the manufacture of resin structures reinforced with fibers as described above, bundles of fibers for reinforcing the resin structure are generally supplied as roving packages or similar materials in which monofilaments with a diameter of 4 to 25 micrometers such as glass fibers, carbon fibers, metallic fibers, or organic fibers are bound with a suitable sizing agent to be flat.
The fiber bundle is taken out from the above package before the bundle is impregnated with a resin by either a taking-from-outside method or a taking-from-inside method. In the taking-from-outside method, a fiber bundle is taken out from the outer circumference of the cylindrical package while the package is rotated. Although this method is advantageous in that the fiber bundle does not twist, increased loads are applied to the fiber bundle because the package itself is rotated, causing nappy splits as a result of breakage of fibers. In addition, when the fiber bundle is released from the package, some fibers tends to remain on the package, resulting in the problem of poor releasability.
By contrast, according to the taking-from-inside method, a fiber bundle is taken out from the inner circumference of the cylindrical package, and lower loads are applied to the fiber bundle which are taken out. Moreover, because a protective cover can be used to prevent crumbling and pollution of the package, it is said that this method is advantageous from the standpoint of workability. Releasability is good, too. However, this method has the drawback that one twist is applied to the fiber bundle after one loop of the fiber bundle is removed from the inner circumference of the package, when the fiber bundle is removed from the inner side of the package which is fixed to a support. Occurrence of twisting in a fiber bundle results in insufficient fiber-loosening, accompanied by insufficient and uneven impregnation with a resin in the manufacture of resin structures reinforced with long fibers, and breakage of fibers in a fiber-loosening step or the like, leaving nappy splits.
Japanese Patent Application Laid-open (kokai) No. 5-84,838 discloses a method of eliminating twisting of a fiber bundle when the bundle is taken from the inside of a package. The method uses an apparatus which contains a table rotatably supported by a frame, a guide roll which is provided in a protruding manner at the center of a table, a tension sensor which is provided in the guide roll for detecting the tension of the fiber bundle applied to the guide roll, and a rotation driving means for rotating the table according to the signal detected by the tension sensor. According to the method of this publication, the tension generated in the fiber bundle when it is taken up from a hollow cylindrical package to the outside is detected, and based on the detected signals, the table is intermittently or continuously rotated in the direction opposite to the direction of rewinding of the fiber bundle to continuously take out a fiber bundle. This method, however, leaves room for improvement since the apparatus is rather complicated, and problems are involved when fiber bundles are continuously drawn out from a plurality of cylindrical fiber bundles.